1. Field of the Invention
The present invention relates to a universal joint of the cross and yoke type or a so-called Cardan or Hooke universal joint.
2. Description of the Prior Art
This type of universal joint is widely used in automotive drive lines, as a joint for a two-piece propeller shaft for instance.
FIG. 1 shows a prior art single Cardan universal joint for a two-piece propeller shaft. The joint is generally indicated by the reference numeral 10 and consists of an input yoke 12 to be connected to a driving shaft section (not shown) and formed at its bifurcate portions with a pair of radial openings 12a which are axially aligned with each other, an output yoke 14 to be connected to a driven shaft section (not shown) and formed at its bifurcate portions with a pair of radial openings 14a which are axially aligned with each other, a cross or cross spider 16 having two pairs of arms 16a and 16b which are respectively aligned to have common axes normal to each other, and four needle bearing assemblies 18 mounted in the openings 12a and 14a and supporting therein the cross arms 16a and 16b so that the input and output yokes 12 and 14 are joined by the cross spider 16 by interposing therebetween the needle bearing assemblies 18.
As shown in an enlarged scale in FIG. 2, each needle bearing assembly 18 consists of a cap 20 covering the cross arm 16a or 16b and having, with respect to the axis of the cross arm 16a or 16b, an inward open end where it is formed with a radially inward flange 20a, and a plurality of needle rollers 22 confined between the cap 20 and the cross arm 16a or 16b. The cap 20 is adapted to be force-fitted in the opening 12a or 14a and prevented from slipping out of the opening 12a or 14a by protruded wall portions 12b or 14b which are formed by caulking after insertion of the cap.
The cap 20 is filled with lubricant for lubricating the needle rollers 22 and the cross arm 16a or 16b. In order to prevent the lubricant from leaking out of the cap 20, an annular sealing member 24 is disposed between the open end of the cap 20 and the cross spider 16. To this end, the cross arm 16a or 16b is formed at its inward end with an annular shoulder 16c which faces the inward flange 20a of the cap 20. The sealing member 24 is adapted to be clamped between the inward flange 20a and the shoulder 16c to provide a seal therebetween, whereby to prevent the lubricant from leaking out of the cap 20 and at the same time prevent entry of foreign matters such as dust and water into the inside of the needle bearing 18.
The sealing member 24 is installed in place as follows. Firstly, it is placed onto the cross arm 16a or 16b and moved axially inwardly of same until it comes in contact with the the shoulder 16c. The bearing assembly 18 is then inserted into the opening 12a or 14a while receiving therein the cross arm 16a or 16b, allowing the sealing member 24 to be clamped between the inward flange 20a of the cap 20 and the shoulder 16c of the cross spider 16. The bearing assembly 18 is prevented from slipping out of the opening 12a or 14a by applying caulking to the wall of the opening 12a or 14a.
The degree of tightness or the amount of compression of the sealing member 24 when installed in place is intimately related to the sealing action and the durability of same. For example, if the amount of compression is too large to be included within predetermined limits a deteriorated durability of the sealing member 24 will result, whereas if too small a deteriorated sealing action will result. Accordingly, special care is required by the sealing member 24 upon installation of same so that the amount of compression is included within the predetermined limits.
However, with the prior art structure, the compression of the sealing member 24 when installed in place tends to vary beyond predetermined limits and therefore an excessive compression or an insufficient compression of the sealing member 24 tends to result. By experiments conducted by the applicant, it was found that such a large variation in the compression of the sealing member 24 results from the fact that the sealing member 24 is formed as an independent part separated from both the cap 20 and the cross spider 16 to have two abuttingly engaging portions and the fact that the compression of the sealing member 24 when installed in place varies depending upon the variation of the state of abutment in which the sealing member 24 abuts upon the inward flange 20a of the cap 20 and further upon the variation of the state of abutment in which the sealing member 24 abuts upon the shoulder 16c of the cross spider 16.